Back grinding adhesive sheet, and method for manufacturing semiconductor wafer

ABSTRACT

Provided is a back grinding adhesive sheet which can adequately protect protrusions provided to a semiconductor wafer, and with which back grinding can be adequately performed. The present invention provides a back grinding adhesive sheet for a semiconductor wafer having protrusions, the back grinding adhesive sheet comprising a non-adhesive cushion layer, and an adhesive layer provided on the cushion layer. The adhesive layer has an opening with a smaller diameter than the diameter of the semiconductor wafer, and the outer edge of the semiconductor wafer is adhered to the adhesive layer such that the protrusions on the semiconductor wafer are positioned inside the opening. The protrusions are protected by the cushion layer when the semiconductor wafer is in the state of being adhered to the adhesive layer. The adhesive sheet satisfies at least one of the following conditions (1)-(2). (1) When the cushion layer is cut out using the dumbbell from JISZ1702 and is stretched 25% at a gauge length of 40 mm and a tensile speed of 300 mm/min, the tensile stress is 2-30N/10 mm. (2) The cushion layer is formed from a thermoplastic resin that has a melt flow rate (JISK7210, 125° C./10.0 kg load) of 0.2-30 g/10 min, and a melting point of 60-110° C.

TECHNICAL FIELD

The present invention relates to an adhesive sheet for back grinding anda method for manufacturing semiconductor wafers using the same.

BACKGROUND ART

When semiconductor wafers are processed, adhesive sheets are attached tothe wafers to protect them from damage. For example, during backgrinding processes for the semiconductor wafer, the adhesive sheet isattached to the wafer to protect a pattern surface thereof. The adhesivesheet is required to have followability to follow unevenness of thepattern surface (bump followability) in terms of adhesiveness to unevenpattern surfaces such as protruding electrodes (bumps) and reliabilityof pattern surface protection.

As an adhesive sheet having the followability, adhesive sheets with athicker adhesive or a flexible resin layer with cushioning propertiesbetween a base film and an adhesive are common in the market. However,in the case of a pattern surface with rough unevenness, risks ofinsufficient followability and adhesive residue increase.

Patent Document 1 discloses an adhesive sheet including a base materialsheet, a non-adhesive part and an adhesive part, in which one side ofthe base material sheet has the non-adhesive part with a diametersmaller than an outer diameter of a semiconductor wafer to be attachedand the adhesive part surrounding the non-adhesive part, and adhesivestrength of the adhesive part at 23° C. is 500 mN or more to preventadhesive residue and to prevent deterioration of protective function.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP2013-211438A

SUMMARY OF INVENTION Technical Problem

In the configuration of Patent Document 1, back grinding of thesemiconductor wafer is performed in a state where only tips of theprotruding electrodes of the semiconductor wafer are in contact with thebase sheet, which may cause damage to the protruding electrodes due toexcessive load applied to the protruding electrodes during the backgrinding.

The present invention was made in consideration of these circumstances.The purpose of the present invention is to provides an adhesive sheetfor back grinding capable of protecting convex portions of asemiconductor wafer properly and preforming the back grinding properly.

Solution to Problem

According to the present invention, there is provided an adhesive sheetfor back grinding of a semiconductor wafer having convex portions,including a non-adhesive cushion layer and an adhesive layer provided onthe cushion layer, in which the adhesive layer includes an opening witha diameter smaller than a diameter of the semiconductor wafer, theadhesive layer is configured to be attached to an outer periphery of thesemiconductor wafer so that the convex portions of the semiconductorwafer are placed in the opening, whereby the convex portions areprotected by the cushion layer in a state where the semiconductor waferis attached to the adhesive layer, and at least one of the followingconditions (1) and (2) is satisfied:

(1) tensile stress of the cushion layer punched out by using a dumbbellaccording to JISZ1702 is 2 to 30N/10 mm when the punched-out cushionlayer is stretched by 25% at a distance between gauge lines of 40 mm anda tensile speed of 300 mm/min; and

-   -   (2) the cushion layer is composed of a thermoplastic resin with        a melt flow rate (JISK7210, 125° C./10.0 kg load) of 0.2 to 30        g/10 min and a melting point of 60 to 110° C.

The present inventors conducted a thorough investigation and found thatit is possible to properly protect the convex portions on thesemiconductor wafer and perform the back grinding by setting the tensilestress of the cushion layer of the adhesive sheet to the above ranges orby setting MFR and viscosity of the thermoplastic resin constituting thecushion layer of the adhesive sheet to the above ranges, and byperforming the back grinding in a state where the adhesive layer isattached to an outer periphery of the semiconductor wafer so that theconvex portions of the semiconductor wafer are placed in the opening andthe convex portions of the semiconductor wafer are protected by thecushion layer.

The following are examples of various embodiments of the presentinvention. The embodiments shown below can be combined with each other.

Preferably, there is provided the adhesive layer, in which the convexportions are protected by being embedded in the cushion layer.

Preferably, there is provided the adhesive layer, in which the adhesivelayer is adhered to the semiconductor wafer under reduced pressure.

Preferably, there is provided the adhesive layer, in which thickness ofthe cushion layer is 50 to 300 μm and thickness of the adhesive layer is1 to 100 μm.

Preferably, there is provided the adhesive layer, in which the adhesivesheet is used in a state where a curable resin and a support film arelaminated onto a cushion layer side of the adhesive sheet.

Preferably, there is provided the adhesive layer, in which the curableresin has a viscosity of 100 to 3,000 mPa·s before curing and Shore Dhardness of 5 to 72 after curing.

Preferably, there is provided the adhesive layer, in which when heightof the convex portion 5 is Td (μm), thickness of the curable resin is(Td+20) to (Td+200) μm.

Preferably, there is provided the adhesive sheet, in which the adhesivesheet includes: a curable resin layer containing the curable resin; andthe support film, in which the curable resin layer is provided on anopposite side of a surface of the adhesive sheet provided with theadhesive layer and between the support film and a surface of the cushionlayer.

Preferably, there is provided the adhesive sheet, in which the adhesivesheet includes a cured resin layer so as to surround the curable resinlayer.

Preferably, there is provided a method for manufacturing a semiconductorwafer using the adhesive sheet, including a frame adhering process, awafer adhering process, a cutting process, a resin curing process, agrinding process, and a peeling process, in which

in the frame adhering process, the adhesive sheet is adhered to a ringframe,

in the wafer adhering process, the adhesive sheet is adhered to asurface of the semiconductor wafer having the convex portions on aperiphery of the semiconductor wafer under reduced pressure,

in the cutting process, the adhesive sheet is cut along the periphery ofthe semiconductor wafer,

in the resin curing process, the curable resin is cured in a state wherethe cushion layer is in contact with the curable resin,

in the grinding process, a backside of the semiconductor wafer isground,

in the peeling process, the adhesive sheet is peeled off from thesemiconductor wafer, and

at least one of the following conditions (A) and (B) is satisfied:

-   -   (A) the above condition is satisfied (1); and    -   (B) the above condition (2) is satisfied, the method further        includes a heating process, and in the heating process, the        cushion layer is heated to 60 to 150° C.

Preferably, there is provided the method for manufacturing thesemiconductor wafer, in which tensile stress of the cushion layerpunched out by using a dumbbell according to JISZ1702 is 2 to 30 N/10 mmwhen the punched-out cushion layer is stretched by 25% at a distancebetween gauge lines of 40 mm and a tensile speed of 300 mm/min.

Preferably, there is provided the method for manufacturing thesemiconductor wafer, in which the curable resin has a viscosity of 100to 3,000 mPa·s before curing and Shore D hardness of 5 to 72 aftercuring.

Preferably, there is provided the method for manufacturing thesemiconductor wafer, in which the method includes a pressing processbetween the wafer adhering process and the resin curing process, inwhich, in the pressing process, the curable resin is pressed and spreadby moving the adhesive sheet while the adhesive sheet faces the curableresin supplied on the support film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D show cross-sectional views for illustrating a method formanufacturing a semiconductor wafer using an adhesive sheet 10 of thefirst and third embodiments of the present invention.

FIGS. 2A to 2E show cross-sectional views for illustrating the methodfor manufacturing the semiconductor wafer using the adhesive sheet 10 ofthe first and third embodiments of the present invention.

FIG. 3 shows a cross-sectional view of an adhesive sheet 10 of thesecond and fourth embodiments of the present invention.

FIGS. 4A to 4C show cross-sectional views for illustrating a method formanufacturing the adhesive sheet 10 of the second and fourth embodimentsof the present invention.

FIGS. 5A to 5D show cross-sectional views for illustrating the methodfor manufacturing the semiconductor wafer using the adhesive sheet 10 ofthe second and fourth embodiments of the present invention.

FIGS. 6A to 6D show cross-sectional views for illustrating the methodfor manufacturing the semiconductor wafer using the adhesive sheet 10 ofthe second and fourth embodiments of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described. Various featuresshown in the following embodiments can be combined with each other. Inaddition, the invention can be made independently for each feature.

1. First Embodiment

1-1. Adhesive Sheet

Adhesive sheet 10 of the first embodiment of the present invention willbe described using FIGS. 1A to 2E. The adhesive sheet 10 of thisembodiment is an adhesive sheet for back grinding of a semiconductorwafer having convex portions, and is a “non-heated” type that isintended to be used without heating. The adhesive sheet 10 of thisembodiment has a non-adhesive cushion layer 1 and an adhesive layer 2provided on the cushion layer 1, and is used for grinding a backside 4 bof a semiconductor wafer 4 having convex portions 5. Preferably, thisadhesive sheet 10 is used in a state where a curable resin 8 and asupport film 7 are laminated onto a cushion layer 1 side of the adhesivesheet 10. Each configuration will be described below.

Cushion Layer 1

The cushion layer 1 is a layer for protecting the convex portions 5 ofthe semiconductor wafer 4, and is preferably configured to have tensilestress of 2 to 30 N/10 mm. When the tensile stress is 2 N/10 mm or more,handling performance of the adhesive sheet 10 becomes good. When thetensile stress is 30 N/10 mm or less, the convex portions 5 of thesemiconductor wafer 4 are easily embedded in the cushion layer 1, andthe convex portions 5 can be properly protected. The tensile stress ofthe cushion layer 1 is preferably 3 to 15 N/10 mm. The tensile stressmeans tensile stress when the cushion layer 1 punched out by using adumbbell according to JISZ1702 is stretched by 25% at a distance betweengauge lines of 40 mm and a tensile speed of 300 mm/min.

Thickness of the cushion layer 1 is preferably 50 to 300 μm, and morepreferably 50 to 100 μm.

The cushion layer 1 is preferably composed of thermoplastic resin. Theconstituent of the thermoplastic resin may be: ionoma resins in whichcarboxyl groups of single material such as ethylene-methacrylicacid-acrylic ester ternary copolymer, ethylene-methacrylic acidcopolymer, and ethylene-acrylic acid copolymer and/or composite materialthereof are cross-linked with metal ions such as sodium ions, lithiumions and magnesium ions; soft polypropylene resins blended withstyrene-butadiene copolymer rubber, styrene-butadiene styrene blockcopolymer rubber, styrene-isoprene-styrene block copolymer rubber,ethylene-propylene rubber or the like; polyurethane; low densitypolyethylene; ethylene-propylene block copolymer; ethylene-propylenerandom copolymer; ethylene-vinyl acetate copolymer; ethylene-methacrylicacid copolymer; ethylene-1 octene copolymer; ethylene-styrene copolymer;ethylene-styrene-diene copolymer; or polybutene, but is not limitedthereto. Among them, the ethylene-styrene copolymer is preferred.

Mass average molecular weight (Mw) of the thermoplastic resin ispreferably 10,000 to 1,000,000, and more preferably 30,000 to 500,000.The mass average molecular weight (Mw) is a polystyrene-equivalent valuemeasured by gel permeation chromatography (GPC) under the measurementconditions described below.

Equipment name: SYSTEM-21 Shodex (manufactured by Showa Denko K.K.)Column: Three PL gel MIXED-B columns in series

Temperature: 40° C.

Detection: Differential refractive index

Solvent: Tetrahydrofuran

Concentration: 2 mass %Calibration curve: Standard polystyrene (PS) (manufactured by PolymerLaboratories Inc.) was used to prepare the calibration curve.

Adhesive Layer 2

The adhesive layer 2 is a layer for adhering the adhesive sheet 10 tothe semiconductor wafer 4, and is composed of adhesives. The adhesivelayer 2 has an opening 2 a with a diameter smaller than the diameter ofthe semiconductor wafer 4. In other words, the adhesive layer 2 has aring shape. The opening 2 a is an area where no adhesive is provided andhas a diameter smaller than the diameter of the semiconductor wafer 4.The diameter of the opening 2 a/diameter of the semiconductor wafer 4 ispreferably 0.950 to 0.995, more preferably 0.960 to 0.990.

The adhesive layer 2 is adhered to an outer periphery 4 a of thesemiconductor wafer 4 so that the convex portions 5 of the wafer 4 areplaced in the opening 2 a. As a result, the convex portions 5 is not incontact with the adhesive, and adhesive residue on the convex portions 5is prevented.

Width of the adhesive layer 2 is preferably 10 to 100 mm, morepreferably 30 to 70 mm. Thickness of the adhesive layer 2 is preferably1 to 100 μm, more preferably 5 to 50 μm.

The constituent of the adhesive can includes: 2-Hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate and the like with hydroxyl groups as (meth)acrylicmonomer or monomer containing functional groups such as butyl(meth)acrylate, 2-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl(meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl(meth)acrylate decyl (meth)acrylate, lauryl (meth)acrylate, methyl(meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, tridecyl(meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl(meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate,dimethyl acrylamide, diethyl acrylamide, acryloyl morpholine andisobornyl acrylate; (meth)acrylic acid, crotonic acid, maleic acid,itaconic acid, fumaric acid, acrylamide N-glycolic acid, cinnamic acidand the like with carboxyl groups; and allyl glycidyl ether,(meth)acrylic acid glycidyl ether and the like with epoxy groups, butare not limited thereto. The adhesive contains preferably a curingagent. The curing agents include polyfunctional isocyanate curing agentsand polyfunctional epoxy curing agents. When the curing agent reactswith the functional group, cross-linked structures with the functionalgroups as base points are formed, which increases cohesive strength ofthe adhesive and suppresses adhesive residue. In addition,(meth)acrylate with one or more (meth)acroylated ends or side chains ofoligomer/polymer such as 1,2-polybutadiene-terminated urethane(meth)acrylate, hydrogenated product thereof,1,4-polybutadiene-terminated urethane (meth)acrylate,polyisoprene-terminated (meth)acrylate, polyester-based urethane(meth)acrylate, polyether-based urethane (meth)acrylate, polyester(meth)acrylate, bis-A epoxy (meth)acrylate may be used.

The adhesive layer 2 can be formed by coating the adhesive on thecushion layer 1 or by applying it on release films and then transferringit to the cushion layer 1, for example, by coating methods such asgeneral comma coating, gravure coating, roll coating and screen coating.

Semiconductor Wafer 4

The semiconductor wafer 4 has convex portions 5. The convex portions 5have any structures that protrude in the out-of-plane direction of thesemiconductor wafer 4. An example of the convex portions 5 is protrudingelectrodes or convex portions of a circuit with concavity and convexity.

The semiconductor wafer 4 includes not only a silicon wafer but also agermanium wafer, a gallium-arsenide wafer, a gallium-phosphorus wafer, agallium-arsenide aluminum wafer. Diameter of the semiconductor wafer 4is preferably 1 to 16 inches, more preferably 4 to 12 inches. Thicknessof the semiconductor wafer 4 is preferably 500 to 800 μm, morepreferably 520 to 775 μm, but is not limited thereto.

Height of the convex portion 5 is preferably 10 to 500 μm, morepreferably 100 to 300 μm. The convex portions 5 are preferably formed bysolder.

The semiconductor wafer 4 has preferably an outer periphery 4 a in whichthe convex portions 5 are not provided. Width of the outer periphery 4 ais preferably 1.0 to 3.0 mm, more preferably 1.5 to 2.5 mm.

Final products using the semiconductor wafers 4 having the convexportions 5 include electronic components for logic, memory, sensor,power supply, etc.

Curable resin 8

The curable resin 8 is a resin that is hardened by stimuli such asenergy rays (e.g., ultraviolet rays) or heat. The curable resin 8 isplaced between the cushion layer 1 and the support film 7.

The curable resin 8 has a viscosity of 100 to 3,000 mPa·s, preferably200 to 1,000 mPa·s before curing. When the viscosity is 100 mPa-s ormore, a surface contact (not point contact) of the curable resin 8prevents air bubbles from entering during a pressing process, resultingin excellent grindability. When the viscosity is 3000 mPa-s or less, thecurable resin 8 is less likely to entrap air bubbles when it flowsbetween the convexe 5 and the adjacent convexe 5, resulting in excellentgrindability. The viscosity is measured using an E-type viscometer underthe conditions of 23° C. and 50 rpm.

The curable resin 8 has preferably Shore D hardness of 5 to 72, morepreferably 5 to 70, even more preferably 10 to 60 after curing. When theShore D hardness is 5 or more, retentivity to retain the convex portions5 is higher, resulting in excellent grindability. When the Shore Dhardness is 72 or less, it is easy to bend the adhesive sheet 10 whenpeeling the adhesive sheet 10 from the semiconductor wafer 4. The ShoreD hardness is measured under the conditions in accordance with JIS K6253.

The curable resin 8 is preferably light curable resin, more preferablyUV curable resin.

The curable resin 8 is preferably based on an acrylic resin. Theconstituent of the curable resin 8 include, for example, butyl(meth)acrylate, 2-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl(meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl(meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, methyl(meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, tridecyl(meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl(meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate,dimethylacrylamide, diethylacrylamide, acryloyl morpholine, isobornylacrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, (meth) acrylic acid, crotonic acid,maleic acid, itaconic acid, fumaric acid, acrylamide N-glycolic acid,cinnamic acid, allyl glycidyl ether, (meth)acrylate glycidyl ether,dimethylacrylamide, diethylacrylamide, acryloyl morpholine, isobornylacrylate.

Furthermore, bifunctional (meth)acrylate monomers includes 1,3-butyleneglycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexadioldi(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, dicyclopentanyl di(meth)acrylate,2-ethyl-2-butyl-propanediol di(meth)acrylate, neopentyl glycol modifiedtrimethylolpropane di(meth)acrylate, stearic acid modifiedpentaerythritoldiacrylate, polypropylene glycol di(meth)acrylate,2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane,2,2-bis(4-(meth)acryloxypropoxyphenyl)propane,2,2-bis(4-(meth)acryloxytetraethoxyphenyl) propane. Trifunctional(meth)acrylate monomers, includes tomethylolpropane tri(meth)acrylate,tris[(meth)acryloxyethyl] isocyanurate. (Meth)acrylate monomers with 4or more functionalities include dimethylolpropane tetra(meth)acrylate,pentaerythritol tetra(meth)acrylate, pentaerythritolethoxytetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate.

Furthermore, (meth)acrylate with one or more (meth)acroylated ends orside chains of oligomer/polymer such as 1,2-polybutadiene-terminatedurethane (meth)acrylate, hydrogenated product thereof,1,4-polybutadiene-terminated urethane (meth)acrylate,polyisoprene-terminated (meth)acrylate, polyester-based urethane(meth)acrylate, polyether-based urethane (meth)acrylate, polyester(meth)acrylate, bis-A epoxy (meth)acrylate may be used. Among them,curable resins containing 1,2-hydrogenated polybutadiene terminalurethane (meth)acrylate, isobornyl acrylate, and diethylacrylamide arepreferred because they can improve the adhesion between the cushionlayer 1 and the support film 7.

Curing shrinkage of the curable resin 8 is preferably 7% or less.

When height of the convex portion 5 is Td (μm), thickness of the curableresin 8 is preferably (Td+20) to (Td+200) μm, more preferably (Td+50) to(Td+150) μm.

Support Film 7

The support film 7 may be any film that can support the curable resin 8and can be made of polyolefins such as ethylene vinyl acetate,polyethylene, polypropylene, polybutene and polybutadiene as well aspolyvinyl chloride, polyethylene terephthalate, polyethylenenaphthalate, polystyrene, polycarbonate, polyimide or the like.

Thickness of the support film 7 is preferably 10 to 300 μm, morepreferably 30-250 μm.

1-2. Method for Manufacturing Semiconductor Wafer

FIGS. 1A to 2E illustrate a method for manufacturing a semiconductorwafer using the adhesive sheet 10. This method includes a frame adheringprocess, a wafer adhering process, a cutting process, a pressingprocess, a resin curing process, a grinding process, and a peelingprocess. The order in which these processes are performed is not limitedthereto, and the order can be swapped as appropriate. Each process isdescribed below.

Frame Adhering Process

As shown in FIGS. 1A and 1B, in the frame adhering process, the adhesivesheet 10 is adhered to the ring frame 3. The ring frame 3 has an opening3 a with a diameter larger than the diameter of the opening 2 a of theadhesive layer 2, and the ring frame 3 can be adhered to the adhesivelayer 2. This allows the adhesive sheet 10 to be held stably in the ringframe 3, making it easier to handle the adhesive sheet 10.

Wafer Adhering Process

As shown in FIGS. 1B and 1C, in the wafer adhering process, the adhesivesheet 10 is adhered to the outer periphery 4 a of the wafer 4 underreduced pressure so that the adhesive sheet 10 is in contact with thesurface with the convex portions 5 of the semiconductor wafer 4. Widthof the adhering surface where the adhesive layer 2 is adhered to thesemiconductor wafer 4 is preferably 1.0 to 3.0 mm, more preferably 1.5to 2.5 mm.

This process can be performed by adhering the adhesive sheet 10 to thesemiconductor wafer 4 in a decompression chamber 16. Pressure in thedecompression chamber 16 should be lower than atmospheric pressure,preferably 50 kPa or less, more preferably 10 kPa or less, even morepreferably 1 kPa or less. Lower limit of the pressure in thedecompression chamber 16 is, for example, 10 Pa, but is not limitedthereto.

By adhering the adhesive sheet 10 to the semiconductor wafer 4 under thereduced pressure in this way, sealed spaces 2 b enclosed by thesemiconductor wafer 4 and the adhesive sheet 10 becomes depressurizedstate.

In that state, when the adhesive sheet 10 adhered to the semiconductorwafer 4 is moved from the decompression chamber 16 and exposed toatmospheric pressure, the cushion layer 1 is pushed by the atmosphericpressure into the sealed spaces 2 b, as shown in FIG. 1D. As a result,the convex portions 5 are embedded in the cushion layer 1, and theconvex portions 5 are protected by the cushion layer 1. The ratio ofheight of the embedded part of the convex portion 5/height of the entireconvex portion 5 is preferably 0.2 to 1, more preferably 0.5 to 1, evenmore preferably 0.8 to 1.

Cutting Process

As shown in FIGS. 1D and 2A, in the cutting process, the adhesive sheet10 is cut along the periphery of the semiconductor wafer 4. As a result,the adhesive sheet 10 adhered to the semiconductor wafer 4 is separatedfrom the ring frame 3.

Pressing Process

As shown in FIGS. 2A and 2B, in the pressing process, the curable resin8 is pressed and spread by moving the adhesive sheet 10 in a state wherethe adhesive sheet 10 faces the curable resin 8 supplied on the supportfilm 7.

In an example, the semiconductor wafer 4 is adsorbed on thedecompression unit 6 having a decompression hole 6 a, and the adhesivesheet 10 is pressed against the curable resin 8 in that state. In thatstate, the curable resin 8 is pressed and spread by moving the adhesivesheet 10 along the surface of the support film 7.

Resin Curing Process

As shown in FIGS. 2B and 2C, in the resin curing process, the curableresin 8 is cured in a state where the cushion layer 1 is placed incontact with the curable resin 8.

In an example, the curable resin 8 can be cured by irradiating energyrays 9 such as ultraviolet rays through the support film 7. This allowsthe adhesive sheet 10 to be held stably on the support film 7.

Grinding Process

As shown in FIGS. 2C and 2D, the grinding process involves grinding thebackside 4 b of the semiconductor wafer 4.

The backside 4 b of the semiconductor wafer 4 is an opposite surface tothe surface on which the convex portions 5 are provided. There are norestrictions on methods for grinding the backside of the wafer, and anyknown grinding method can be used. The grinding is preferably performedwhile water is applied to the wafer and a grinding wheel (e.g., diamondwheel) to cool them down. Thickness of the wafer made thinner by thegrinding is preferably 300 μm or less, more preferably 50 μm or less.

During back grinding, the convex portions 5 are easily damaged becausean in-plane directional load of the semiconductor wafer 4 is applied tothe convex portions 5. However, in this embodiment, since at least someconvex portions 5 are embedded in the cushion layer 1 and the hardenedcurable resin 8, the convex 5 is hardly damaged because the convexportions 5 are stably supported by the cushion layer 1 and the hardenedcurable resin 8. The curable resin 8 can be omitted. In such a case, theconvex portions 5 are supported by the cushion layer 1.

Peeling Process

As shown in FIGS. 2D and 2E, in the peeling process, the adhesive sheet10 is peeled off from the semiconductor wafer 4. The peeling of theadhesive sheet 10 can be performed by curving the adhesive sheet 10 inthe direction in which the sheet 10 moves away from the semiconductorwafer 4.

This completes the back grinding process of the semiconductor wafer 4.When the back grinding is performed using an adhesive sheet in such aform that the convex portions 5 are in contact with the adhesive, theadhesive may adhere to the convex portions 5. However, in thisembodiment, adhesion of the adhesive to the convex portions 5 issuppressed because the convex portions 5 are not in contact with theadhesive layer 2.

2. Second Embodiment

2-1. Adhesive Sheet

In the first embodiment, the adhesive sheet 10 includes the cushionlayer 1 and the adhesive layer 2. In the second embodiment, as shown inFIG. 3, the adhesive sheet 10 further includes a curable resin layer 12and the support film 7.

The curable resin layer 12 is in an uncured state and is the same as thecurable resin of the first embodiment. The support film 7 is the same asthe support film 7 of the first embodiment. An annular cured resin layer22 is provided around the curable resin layer 12. The cured resin layer22 can be formed by curing the curable resin. Assuming that the heightof the convex portion 5 is Td (μm), each thickness of the curable resinlayer 12 and the cured resin layer 22 is preferably (Td+20) to (Td+200)μm, more preferably (Td+50) to (Td+150) μm.

A method for manufacturing the adhesive sheet 10 of this embodiment willbe described using FIGS. 4A to 4C. First, as shown in FIG. 4A, alaminate is formed by laminating the curable resin layer 12, cushionlayer 1, adhesive layer 2, and a release liner 13 on the support film 7in this order. The release liner 13 is used to protect the adhesivelayer 2 and is peeled off in use of the adhesive sheet 10. A mask 14 isused to shield energy rays in an area covered by the mask 14.

Second, the mask 14 is placed on the release liner 13, and the energyrays 9 are irradiated to the curable resin layer 12 through the mask 14.The mask 14 is used to shield the energy rays 9 in the area covered bythe mask 14. As shown in FIG. 4b , the curable resin layer 12 cures inthe area not covered by the mask 14 to become the cured resin layer 22.The support film 7 is bonded to the cushion layer 1 via the cured resinlayer 22. The curable resin layer 12 is provided in the space surroundedby the support film 7, the cured resin layer 22, and the cushion layer1. The mask 14 may be placed on the support film 7, and the energy rays9 may be irradiated from the support film 7 side.

Third, as shown in FIG. 4C, the adhesive sheet 10 of this embodiment isobtained by cutting the laminate along the periphery of the adhesivelayer 2.

2-2. Method for Manufacturing Semiconductor Wafer

A method for manufacturing the semiconductor wafers using the adhesivesheet 10 of this embodiment will be described using FIGS. 5A to 6D. Thismanufacturing method includes a frame adhering process, a wafer adheringprocess, a resin curing process, a cutting process, a grinding process,and a peeling process. The order in which these processes are performedis not limited thereto, and the order can be swapped as appropriate.Each process will be described below. In the following explanation, theexplanations in common with the first embodiment are not repeated.

Frame Adhering Process

As shown in FIGS. 5A to 5B, in the frame adhering process, the adhesivesheet 10 is adhered to the ring frame 3 as in the first embodiment.

Wafer Adhering Process

As shown in FIGS. 5B and 5C, in the wafer adhering process, the adhesivesheet 10 is adhered to the outer periphery 4 a of the semiconductorwafer 4 under reduced pressure (in the decompression chamber 16) so thatthe adhesive sheet 10 is in contact with the surface with the convexportions 5 of the semiconductor wafer 4, as in the first embodiment. Byadhering the adhesive sheet 10 to the semiconductor wafer 4 under thereduced pressure, sealed spaces 2 b enclosed by the semiconductor wafer4 and the adhesive sheet 10 becomes depressurized state.

In that state, when the adhesive sheet 10 adhered to the semiconductorwafer 4 is moved from the decompression chamber 16 and exposed toatmospheric pressure, the cushion layer 1 is pushed by the atmosphericpressure into the sealed spaces 2 b, as shown in FIG. 5D. As a result,the convex portions 5 are embedded in the cushion layer 1, and theconvex portions 5 are protected by the cushion layer 1.

Resin Curing Process

As shown in FIGS. 6A and 6B, in the resin curing process, the curableresin layer 12 is cured in a state where the cushion layer 1 is placedin contact with the curable resin layer 12.

In an example, the curable resin layer 12 can be cured by irradiatingenergy rays 9 such as ultraviolet rays through the support film 7 to thecurable resin layer 12 in a state where the semiconductor wafer 4 ispressed against the curable resin layer 12 using a pressure unit 26. Asa result, the curable resin layer 12 becomes the cured resin layer 22,and the cushion layer 1 is stably held. The decompression unit 6 of thefirst embodiment can be used as the pressure unit 26.

Cutting Process

As shown in FIGS. 6B and 6C, in the cutting process, the adhesive sheet10 is cut along the periphery of the semiconductor wafer 4. As a result,the adhesive sheet 10 adhered to the semiconductor wafer 4 is separatedfrom the ring frame 3.

Grinding Process

As shown in FIG. 6C, the grinding process involves grinding the backside4 b of the semiconductor wafer 4, as in the first embodiment.

Peeling Process

As shown in FIGS. 6C and 6D, in the peeling process, the adhesive sheet10 is peeled off from the semiconductor wafer 4, as in the firstembodiment.

3. Third Embodiment

3-1. Adhesive Sheet

Basic configuration of the adhesive sheet 10 of this embodiment is thesame as that of the first embodiment, but the adhesive sheet 10 of thisembodiment is a “heated” type that is supposed to be used with heating.The adhesive sheet 10 of this embodiment differs from that of the firstembodiment in the thermoplastic resin of the cushion layer 1.

The thermoplastic resin of the cushion layer 1 of this embodiment has amelt flow rate (MFR) of 0.2 to 30 g/10 min. When the MFR is 0.2 g/10 minor more, it has excellent followability to the convex portions 5 andexcellent grindability. When the MFR is 30 g/10 min or less, thefollowability to the convex portions 5 is not too high, resulting inexcellent peelability. The MFR is preferably 0.3 to 20 g/10 min. The MFRis measured under the conditions of 125° C./10.0 kg load according toJIS K7210.

Melting point of the thermoplastic resin is 60 to 110° C. When themelting point is 60° C. or more, the followability to the convexportions 5 is not too high, resulting in excellent peelability. When themelting point is 110° C. or less, it has excellent followability to theconvex portions 5 and excellent grindability. The melting point ispreferably 70 to 90° C. The melting point is measured under theconditions in accordance with JIS K7121.

Thickness of the cushion layer 1 is preferably 50 to 300 μm, morepreferably 70 to 250 μm.

The constituent of the thermoplastic resin may be: ionoma resins inwhich carboxyl groups of single material such as ethylene-methacrylicacid-acrylic ester ternary copolymer, ethylene-methacrylic acidcopolymer, and ethylene-acrylic acid copolymer and/or composite materialthereof are cross-linked with metal ions such as sodium ions, lithiumions and magnesium ions; soft polypropylene resins blended withstyrene-butadiene copolymer rubber, styrene-butadiene styrene blockcopolymer rubber, styrene-isoprene-styrene block copolymer rubber,ethylene-propylene rubber or the like; low density polyethylene;ethylene-propylene block copolymer; ethylene-propylene random copolymer;ethylene-vinyl acetate copolymer; ethylene-methacrylic acid copolymer;ethylene-loctene copolymer; or polybutene, but is not limited thereto.Among them, the ionoma resin is preferred.

Mass average molecular weight (Mw) of the thermoplastic resin ispreferably 10,000 to 1,000,000, and more preferably 50,000 to 500,000.

Softening temperature (JIS K7206) of the thermoplastic resin ispreferably 45 to 85° C., more preferably 55 to 75° C.

The melting point (JIS K7121) of the thermoplastic resin is preferably60 to 110° C., more preferably 80 to 100° C.

The melt flow rate (MFR) (JIS K7210, 125° C./10.0 kg load) of thethermoplastic resin is preferably 0.2 to 30 g/10 min, more preferably0.3 to 10 g/10 min.

3-2. Method for Manufacturing Semiconductor Wafer

A method for manufacturing a semiconductor wafer using the adhesivesheet 10 of this embodiment will be described. This method includes aframe adhering process, a wafer adhering process, a heating process, acutting process, a resin curing process, a grinding process, and apeeling process. The order in which these processes are performed is notlimited thereto, and the order can be swapped as appropriate. Eachprocess is described below. In the following explanation, theexplanations in common with the first embodiment are not repeated. Theexplanations of the frame adhering process, cutting process, resincuring process, grinding process, and peeling process are the same as inthe first embodiment, so they will not be repeated here.

Wafer adhering process and heating process

As shown in FIGS. 1B and 1C, in the wafer adhering process, the adhesivesheet 10 is adhered to the outer periphery 4 a of the wafer 4 underreduced pressure so that the adhesive sheet 10 is in contact with thesurface with the convex portions 5 of the semiconductor wafer 4, as inthe first embodiment.

In that state, when the adhesive sheet 10 adhered to the semiconductorwafer 4 is moved from the decompression chamber 16 and exposed toatmospheric pressure, the cushion layer 1 is pushed by the atmosphericpressure into the sealed spaces 2 b. When the cushion layer 1 is notheated, it is very rigid, and the cushion layer 1 hardly enters thesealed spaces 2 b. On the other hand, when the cushion layer 1 is heatedto 60 to 150° C. in the heating process, the cushion layer 1 is softenedand enters the sealed spaces 2 b as shown in FIG. 1D. As a result, theconvex portions 5 are embedded in the cushion layer 1, and the convexportions 5 are protected by the cushion layer 1. The ratio of height ofthe embedded part of the convex portion 5/height of the entire convexportion 5 is preferably 0.2 to 1, more preferably 0.5 to 1, even morepreferably 0.8 to 1. Heating temperature of the cushion layer 1 ispreferably 80 to 120° C. Heating time of the cushion layer 1 ispreferably 3 to 120 seconds, more preferably 5 to 60 seconds.

The heating of the cushion layer 1 may be performed before or after thesemiconductor wafer 4 is adhered to the adhesive sheet 10. The heatingmay be performed in the decompression chamber 16 or outside thedecompression chamber 16.

4. Fourth Embodiment

4-1. Adhesive Sheet Basic configuration of the adhesive sheet 10 of thisembodiment is the same as that of the second embodiment, but theadhesive sheet 10 of this embodiment is a “heated” type that is supposedto be used with heating. The adhesive sheet 10 of this embodimentdiffers from that of the first embodiment in the thermoplastic resin ofthe cushion layer 1, and is the same thermoplastic resin as thatdescribed in the third embodiment.

4-2. Method for Manufacturing Semiconductor Wafer

A method for manufacturing the semiconductor wafers using the adhesivesheet 10 of this embodiment will be described. This manufacturing methodincludes a frame adhering process, a wafer adhering process, a heatingprocess, a resin curing process, a cutting process, a grinding process,and a peeling process. The order in which these processes are performedis not limited thereto, and the order can be swapped as appropriate.Each process will be described below. In the following explanation, theexplanations in common with the second embodiment are not repeated. Theexplanations of the frame adhering process, resin curing process,cutting process, grinding process, and peeling process are the same asin the first embodiment, so they will not be repeated here.

Wafer Adhering Process and Heating Process

As shown in FIGS. 5B and 5C, in the wafer adhering process, the adhesivesheet 10 is adhered to the outer periphery 4 a of the wafer 4 underreduced pressure (in the decompression chamber 16) so that the adhesivesheet 10 is in contact with the surface with the convex portions 5 ofthe semiconductor wafer 4, as in the first embodiment. By adhering theadhesive sheet 10 to the semiconductor wafer 4 under the reducedpressure, sealed spaces 2 b enclosed by the semiconductor wafer 4 andthe adhesive sheet 10 becomes depressurized state.

In that state, when the cushion layer 1 is heated to 60 to 150° C. andthen the adhesive sheet 10 adhered to the semiconductor wafer 4 is movedfrom the decompression chamber 16 and exposed to atmospheric pressure,the cushion layer 1 is pushed by the atmospheric pressure into thesealed spaces 2 b, as shown in FIG. 1D. As a result, the convex portions5 are embedded in the cushion layer 1, and the convex portions 5 areprotected by the cushion layer 1.

EXAMPLES 1. Example of an Adhesive Sheet (Non-Heated Type)

Using adhesive sheets 10 with the same configuration as the firstembodiment and with the following tensile stresses of thermoplasticresins and viscosities and Shore hardnesses of UV-curable resins,backsides of semiconductor wafers 4 were ground to evaluate bumpfollowability, air bubble contamination, peelability, grindability(TTV), handling performance and comprehensive judgment.

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 12 Thermoplastic Tensile stress2 3 15 30 3 3 3 3 3 3 3 3 resin (N/10 mm) UV-curable Viscosity 470 470470 470 110 230 1270 2850 580 620 240 220 resin (mPa · s) Shore D 15 1515 15 58 44 13 11 5 11 61 72 hardness Evaluation Bump Great Great GreatGood Great Great Great Great Great Great Great Great followability Airbubble Great Great Great Great Good Great Great Good Great Great GreatGreat contamination Peelability Great Great Great Great Great GreatGreat Great Great Great Great Good Grindability Great Great Great GreatGood Great Great Good Good Great Great Great (TTV) Handling Good GreatGreat Great Great Great Great Great Great Great Great Great performanceComprehensive Good Great Great Good Good Great Great Good Good GreatGreat Good judgment

TABLE 2 Comparative Example Table 2 1 2 Thermoplastic resin Tensilestress (N/10 mm) 1 40 UV-curable resin Viscosity (mPa · s) 470 470 ShoreD hardness 15 15 Evaluation Bump followability Great Poor Air bubblecontamination Great Great Peel ability Great Great Grindability (TTV)Great Great Handling performance Poor Great Comprehensive judgment PoorPoor

1-1. Manufacturing of Adhesive Sheet 10

Each adhesive sheet 10 of the examples and comparative examples wasmanufactured by forming an annular adhesive layer 2 having an opening 2a on the cushion layer 1. Thermoplastic resin constituting each cushionlayer 1 was prepared to have tensile stress shown in Tables 1 and 2. Thetensile stress of the thermoplastic resin is a tensile stress of thecushion layer 1 when the cushion layer 1 punched out by using a dumbbellaccording to JISZ1702 is stretched by 25% at a distance between gaugelines of 40 mm and a tensile speed of 300 mm/min.

The constituent of each thermoplastic resin was ethylene-styrenecopolymer, and the tensile stress thereof was varied by changing thecontent ratio of each constituent unit of ethylene monomer unit andstyrene monomer unit. The constituent of the adhesive constituting eachadhesive layer 2 was 1,2-hydrogenerated polybutadiene terminatedurethane (meth)acrylate.

Thickness of each cushion layer 1 was 50 μm. Thickness of each adhesivelayer 2 was 10 μm. Width of each adhesive layer 2 was 37 mm.

1-2. Back Grinding of Semiconductor Wafer

Using each adhesive sheet 10 fabricated above, the backside of eachsemiconductor wafer 4 was ground by the following method.

First, the adhesive sheet 10 was attached to the ring frame 3. Next, theadhesive sheet 10 was adhered to the outer periphery 4 a of the wafer 4in the decompression chamber 16 so that the adhesive sheet 10 was incontact with the surface with the convex portions 5 of the semiconductorwafer 4. The semiconductor wafer 4 had 8 inches in diameter, and 725 μmin thickness, and had 230 μm high bumps (protruding electrodes) formedin an area other than 3.0 mm periphery. Width of the adhering surfacewhere the semiconductor wafer 4 was adhered to the adhesive layer 2 was2.0 mm. Pressure in the decompression chamber 16 was 100 Pa.

Next, the adhesive sheet 10 to which the semiconductor wafer 4 wasadhered was moved from the decompression chamber 16.

Next, each adhesive sheet 10 was cut along the periphery of therespective semiconductor wafer 4, and the ring frame 3 was separatedfrom the respective adhesive sheet 10.

Next, the curable resin 8 was pressed and spread by moving the adhesivesheet 10 in the in-plane direction of the support film 7 in a statewhere the adhesive sheet 10 faced the curable resin 8 supplied on thesupport film 7. The curable resins 8 were used with the viscosity andShore D hardness shown in Table 1. The viscosity of the curable resin 8before curing was measured using an E-type viscometer at 23° C. and 50rpm. The Shore D hardness of the curable resin 8 after curing wasmeasured under the conditions of JIS K 6253.

The constituent of the curable resin 8 was composed of 1,2-hydrogenatedpolybutadiene terminal urethane (meth)acrylate, isobornyl acrylate, anddiethylacrylamide, and the viscosity and Shore D hardness were varied bychanging each constituent.

Next, the curing resin 8 was cured in a state where the cushion layer 1was placed in contact with the curable resin 8. The curing resin 8 wascured by irradiating UV light from the support film 7 side to the curingresin so that the integrated light intensity at a wavelength of 365 nmwas 2000 mJ/cm².

Next, the backside of the semiconductor wafer 4 was ground until thethickness of the wafer 4 was 200 μm. The back grinding was performedusing a polishing machine (DFG-841 back grinder manufactured by DISCOCorporation).

Peeling Process

Next, each adhesive sheet 10 was peeled off from the respectivesemiconductor wafer 4.

1-3. Evaluation

The following method was used to evaluate the bump followability, airbubble contamination, peelability, grindability (TTV), handlingperformance and comprehensive judgment. The evaluation results are shownin Tables 1 and 2.

Bump Followability

The bump followability was evaluated from the rate of followability(rate of followability=(Distance that the cushion layer 1 followed alongheight of bump/height of bumps)) using the following criteria.

Great: Rate of followability is 80% or moreGood: Rate of followability is 71% to 79%.Poor: Rate of followability is 70% or less

Air Bubble Contamination

The air bubble contamination was evaluated based on the number of airbubbles with a diameter of 1 mm or more, using the following criteria.

Great: Number of air bubbles is 10 or lessGood: Number of bubbles is 11 to 30Poor: Number of bubbles is 31 or more

Peelability

The peelability was evaluated based on the adhesive strength to themirror surface of the silicon wafer measured in accordance with JIS Z0237, using the following criteria.

Great: Adhesive strength is 1.0 N/20 mm or lessGood: Adhesive strength is 1.1 to 2.0 N/20 mmPoor: Adhesive strength is 2.1 N/20 mm or more

Grindability (TTV)

The grindability (TTV: maximum thickness—minimum thickness) wasevaluated by measuring the thickness accuracy of the wafer surface usingSemDex (thickness accuracy measurement device, ISIS Co., Ltd.), usingthe following criteria.

Great: TTV 5 μm or less

Good: TTV 6 to 15 μm

Poor: TTV 16 μm or more

Handling Performance

The handling performance was evaluated based on difference between theset width and the measured width of the adhering surface having theadhesive sheet 10 attached to the semiconductor wafer 4, using thefollowing criteria.

Great: Set width—width of adhering surface is −0.5 mm or more to +0.5 mmor lessGood: Set sidth—width of adhering surface is −1.0 mm to −0.5 mm or +0.5mm to +1.0 mmPoor: Set width—width of adhering surface is less than −1.0 mm or morethan +1.0 mm

Comprehensive Judgment

The comprehensive judgment was based on the following criteria.

Great: All items are “Great”.Good: At least one item is “Good” and no item is“Poor”.Poor: At least one item is “Poor”.

1-4. Results

All the examples showed excellent results in all the evaluation items.On the other hand, all the comparative examples did not showsatisfactory results in at least one of the evaluation items.

2. Example of Adhesive Sheet (Heated Type)

Using adhesive sheets 10 with the same configuration as the thirdembodiment and with the following MFRs and melting points of thethermoplastic resins and the viscosities and Shore hardnesses of theUV-curable resins, backsides of semiconductor wafers 4 were ground toevaluate bump followability, air bubble contamination, peelability,grindability (TTV) and comprehensive judgment.

TABLE 3 Example 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29Thermo- MFR 0.2 0.3 11 18 28 3 5 7 2 7 7 7 7 7 7 7 7 plastic (g/10 min)resin Melting 89 86 84 83 88 62 72 92 107 84 84 84 84 84 84 84 84 point(° C.) UV- Viscosity 470 470 470 470 470 470 470 470 470 110 230 12702850 580 620 240 220 curable (mPa · s) resin Shore D 15 15 15 15 15 1515 15 15 58 44 13 11 5 11 61 72 hardness Evalua- Bump Good Great GreatGreat Great Great Great Great Good Great Great Great Great Great GreatGreat Great tion followability Air bubble Great Great Great Great GreatGreat Great Great Great Good Great Great Good Great Great Great Greatcontamination Peelability Great Great Great Great Good Good Great GreatGreat Great Great Great Great Great Great Great Good Grindability GoodGreat Great Great Great Great Great Great Good Good Great Great GoodGood Great Great Great (TTV) Comprehensive Good Great Great Great GoodGood Great Great Good Good Great Great Good Good Great Great Goodjudgment

TABLE 4 Comparative Example Table 4 3 4 5 6 Thermoplastic MFR (g/10 min)0.1 33 1 25 resin Melting point 90 91 53 114 (° C.) UV-curable resinViscosity (mPa · s) 470 470 470 470 Shore D hardness 15 15 15 15Evaluation Bump followability Poor Great Great Poor Air bubblecontamination Great Great Great Great Peelability Great Poor Poor GreatGrindability (TTV) Poor Great Great Poor Comprehensive judgment PoorPoor Poor Poor

2-1. Manufacturing of Adhesive Sheet 10

Each adhesive sheet 10 of the examples and comparative examples wasmanufactured by forming an annular adhesive layer 2 having an opening 2a on the cushion layer 1. The MFR and melting point of thermoplasticresin constituting each cushion layer 1 are listed in Tables 3 and 4.

The constituent of each thermoplastic resin was metal ion-crosslinkedethylene-methacrylic acid copolymer, and the MFR and melting point werevaried by changing the copolymer constituent and mass average molecularweight.

The constituent of the adhesive constituting each adhesive layer 2 is1,2-hydrogenerated polybutadiene terminated urethane (meth)acrylate.

Thickness of each cushion layer 1 was set 150 μm. Thickness of eachadhesive layer 2 was 10 μm. Width of each adhesive layer 2 was 37 mm.

2-2. Back Grinding of Semiconductor Wafer

Using each adhesive sheet 10 fabricated above, the backside of eachsemiconductor wafer 4 was ground by the following method.

First, the adhesive sheet 10 was attached to the ring frame 3. Next, theadhesive sheet 10 was adhered to the outer periphery 4 a of the wafer 4in the decompression chamber 16 so that the adhesive sheet 10 was incontact with the surface with the convex portions 5 of the semiconductorwafer 4. The semiconductor wafer 4 had 8 inches in diameter, and 725 μmin thickness, and had 230 μm high bumps (protruding electrodes) formedin an area other than 3.0 mm periphery. Width of the adhering surfacewhere the adhesive layer 2 was adhered to the semiconductor wafer 4 was2.0 mm. Pressure in the decompression chamber 16 was 100 Pa. In thedecompression chamber 16, the cushion layers 1 were heated to 100° C.

Next, the adhesive sheet 10 to which the semiconductor wafer 4 wasadhered was moved from the decompression chamber 16.

Next, the adhesive sheet 10 was cut along the periphery of therespective semiconductor wafer 4, and each ring frame 3 was separatedfrom the respective adhesive sheet 10.

Next, the curable resin 8 was pressed and spread by moving the adhesivesheet 10 in the in-plane direction of the support film 7 in a statewhere the adhesive sheet 10 faced the curable resin 8 supplied on thesupport film 7. The curable resins 8 were used with the viscosity andShore D hardness shown in Table 3. The viscosity of the curable resin 8before curing was measured using an E-type viscometer at 23° C. and 50rpm. The Shore D hardness of the curable resin 8 after curing wasmeasured according to JIS K 6253.

The constituent of the curable resin 8 was composed of 1,2-hydrogenatedpolybutadiene terminal urethane (meth)acrylate, isobornyl acrylate, anddiethylacrylamide, and the viscosity and Shore D hardness were varied bychanging each constituent.

Next, the curing resin 8 was cured in a state where the cushion layer 1was placed in contact with the curable resin 8. The curing resin 8 wascured by irradiating UV light from the support film 7 side to the curingresin so that the integrated light intensity at a wavelength of 365 nmwas 2000 mJ/cm².

Next, the backside of the semiconductor wafer 4 was ground until thethickness of the wafer 4 was 200 μm. The back grinding was performedusing a polishing machine (DFG-841 back grinder manufactured by DISCOCorporation).

Peeling Process

Next, each adhesive sheet 10 was peeled off from the respectivesemiconductor wafer 4.

2-3. Evaluation

The following method was used to evaluate the bump followability, airbubble contamination, peelability, grindability (TTV) and comprehensivejudgment. The evaluation criteria are as explained in “1-3. Evaluation”.The evaluation results are shown in Tables 3 and 4.

2-4. Results

All the examples showed excellent results in all the evaluation items.On the other hand, all the comparative examples did not showsatisfactory results in at least one of the evaluation items.

EXPLANATION OF THE CODE

-   1: Cushion layer-   2: Adhesive layer-   2 a: Opening-   2 b: Sealed space-   3: Ring frame-   3 a: Opening-   4: Semiconductor wafer-   4 a: Outer periphery-   4 b: Backside-   5: Convex portion-   6: Decompression unit-   6 a: Decompression hole-   7: Support film-   8: Curable resin-   9: Energy ray-   10: Adhesive sheet-   12: Curable resin layer-   13: Release liner-   14: Mask-   16: Decompression chamber-   22: Cured resin layer-   26: Pressure unit

1. An adhesive sheet for back grinding of a semiconductor wafer havingconvex portions, comprising a non-adhesive cushion layer and an adhesivelayer provided on the cushion layer, wherein the adhesive layercomprises an opening with a diameter smaller than a diameter of thesemiconductor wafer, the adhesive layer is configured to be attached toan outer periphery of the semiconductor wafer so that the convexportions of the semiconductor wafer are placed in the opening, wherebythe convex portions are protected by the cushion layer in a state wherethe semiconductor wafer is attached to the adhesive layer, and at leastone of the following conditions (1) and (2) is satisfied: (1) tensilestress of the cushion layer punched out by using a dumbbell according toJISZ1702 is 2 to 30N/10 mm when the punched-out cushion layer isstretched by 25% at a distance between gauge lines of 40 mm and atensile speed of 300 mm/min; and (2) the cushion layer is composed of athermoplastic resin with a melt flow rate (JISK7210, 125° C./10.0 kgload) of 0.2 to 30 g/10 min and a melting point of 60 to 110° C.
 2. Theadhesive sheet according to claim 1, wherein the convex portions areprotected by being embedded in the cushion layer.
 3. The adhesive sheetaccording to claim 1, wherein the adhesive layer is attached thesemiconductor wafer under reduced pressure.
 4. The adhesive sheetaccording to claim 1, wherein thickness of the cushion layer is 50 to300 μm and thickness of the adhesive layer is 1 to 100 μm.
 5. Theadhesive sheet according to claim 1, wherein the adhesive sheet is usedin a state where a curable resin and a support film are laminated onto acushion layer side of the adhesive sheet.
 6. The adhesive sheetaccording to claim 5, wherein the curable resin has a viscosity of 100to 3,000 mPa·s before curing and Shore D hardness of 5 to 72 aftercuring.
 7. The adhesive sheet according to claim 5, wherein when heightof the convex portion 5 is Td (μm), thickness of the curable resin is(Td+20) to (Td+200) μm.
 8. The adhesive sheet according to claim 5,further comprising: a curable resin layer containing the curable resin;and the support film, wherein the curable resin layer is provided on anopposite side of a surface of the adhesive sheet provided with theadhesive layer and between the support film and a surface of the cushionlayer.
 9. The adhesive sheet according to claim 8, further comprising acured resin layer so as to surround the curable resin layer.
 10. Amethod for manufacturing a semiconductor wafer using the adhesive sheetaccording to claim 1, comprising a frame adhering process, a waferadhering process, a cutting process, a resin curing process, a grindingprocess, and a peeling process, wherein in the frame adhering process,the adhesive sheet is adhered to a ring frame, in the wafer adheringprocess, the adhesive sheet is adhered to a surface of the semiconductorwafer having the convex portions on a periphery of the semiconductorwafer under reduced pressure, in the cutting process, the adhesive sheetis cut along the periphery of the semiconductor wafer, in the resincuring process, the curable resin is cured in a state where the cushionlayer is in contact with the curable resin, in the grinding process, abackside of the semiconductor wafer is ground, in the peeling process,the adhesive sheet is peeled off from the semiconductor wafer, and atleast one of the following conditions (A) and (B) is satisfied: (A) theabove condition is satisfied (1); and (B) the above condition (2) issatisfied, the method further comprises a heating process, and in theheating process, the cushion layer is heated to 60 to 150° C.
 11. Themethod for manufacturing the semiconductor wafer according to claim 10,wherein tensile stress of the cushion layer punched out by using adumbbell according to JISZ1702 is 2 to 30 N/10 mm when the punched-outcushion layer is stretched by 25% at a distance between gauge lines of40 mm and a tensile speed of 300 mm/min.
 12. The method formanufacturing the semiconductor wafer according to claim 10, wherein thecurable resin has a viscosity of 100 to 3,000 mPa·s before curing andShore D hardness of 5 to 72 after curing.
 13. The method formanufacturing the semiconductor wafer according to claim 10 furthercomprising a pressing process between the wafer adhering process and theresin curing process, wherein, in the pressing process, the curableresin is pressed and spread by moving the adhesive sheet while theadhesive sheet faces the curable resin supplied on the support film.